A modern quantitative fluorescent microscopy system with the capability for quantification of fluorescent, reflected, emitted, and transmitted light is described. The instrument will serve a broad range of biological scientists in the East Tennessee area and will allow them access to modern microscopic instrumentation. In this system a highly sensitive television camera is combined with fluorescence microscopy and photometric microscopy to enable the examination, localization, and quantification of biologically important compounds in living cells. Using very small amounts of excitation energy, damage to the living cell is minimal, and visualization of fluorescent probes is possible for a period up to 24 hours without bleaching. Proposed research projects using this modern microscopic instrumentation are manifold and include: the study of peptide transport and utilization in yeast; the interaction of yeast mating factor with target cells; the interaction of angiotensin with cultured endothelial cells; the metabolism of acetylcholine receptor in a nonmuscle cell; the turnover of acetylcholine receptor in cultured myotubes; the interaction of phospholipid vesicles (liposomes) with animal cells; gonadotropin receptor regeneration and metabolism; the distribution, internalization, and metabolism of ouabain receptors, the direct visualization of endocytosis and membrane cycling, the expression of specific herpes simplex virus glycoproteins on the surface of infected cells; the study of several aspects of the symbiotic relationship between a strain of amoeba and its endosymbiotic bacteria; the study of the ultra-structure and development of extracellular matrices and photoreceptor apparatus and organelles involved in hetrophagy in algalflagellates; and the study of chromatin structure.